Optical feedback to monitor and control laser rock removal

ABSTRACT

Methods, systems, and devices related to downhole wellbore operations such as drilling and completing wells in an earth formation that include a laser device. The method includes lasing a rock and detecting an optical response of the lased rock. It can be determined from the optical response whether the lased rock is responding as specified (e.g. spalling, melting, etc.) If the lased rock is not responding as specified, one or more laser parameters are adjusted to achieve the specified response. Spalling is determined by the detection of sparks, or other light that erratically changes in intensity over time, by an optical detector. The detection of steady light may indicate other types of rock removal mechanisms, such as melt or dissociation.

FIELD

The present disclosure relates generally to rock removal using a laser,and more particularly, to adjusting laser power of rock removal based onoptical feedback.

BACKGROUND

Once a wellbore has been drilled and one or more zones of interest havebeen reached, a well casing is run into the wellbore and is set in placeby injecting cement or other material into the annulus between thecasing and the wellbore. The casing, cement and formation are thenperforated to enable flow of fluid from the formation into the interiorof the casing. In some cases, the casing can be omitted.

SUMMARY

Aspects of the present disclosure are directed to systems, apparatuses,and methods for removing subterranean rock with a laser. Certain aspectsof the implementations include, lasing subterranean rock around a wellbore from inside the well bore. Emissions, such as optical and/orthermal emissions, can be detected from the lased rock. It can bedetermined whether the detected emissions from the lased rock indicatesa specified material removal mechanism. If the detected emissions do notindicate the specified material removal mechanism is taking place, oneor more laser cutting parameters can be adjusted until emissionsdetected from the lased rock indicates the specified material removalmechanism.

Certain aspects of the implementations are directed to a well lasersystem for use in a subterranean well. The system may include a laserapparatus configured to produce a laser beam, and direct the laser beamtowards a subterranean rock. An optical detector may also be includedand may be configured to detect light emitted from the rock. Acontroller may be communicatively coupled to the optical detector. Thecontroller configured to receive a signal from the optical detector,determine from the signal whether the rock is responding as specified,and adjust a parameter of the laser if the rock is not responding asspecified.

Certain aspects of the implementations are directed to a well apparatusfor rock removal. The well apparatus may include a laser tool configuredfor insertion into the well and to direct laser energy onto rock. Thelaser tool may include a laser or may include optics that direct a laserbeam produced by a terrestrially-located laser. The apparatus may alsoinclude a detector configured for insertion into the well and to detectemissions emitted from the rock. A controller can be configured toadjust power of a laser based on emissions detected from the rock.

Certain aspects of the implementations may include assessing an opticalprofile of the emissions detected from the lased rock for characteristicproperties of the specified material removal mechanisms. Acharacteristic property of a material removal mechanism may include adetection of steady emissions. In other instances, a characteristicproperty of a specified material removal mechanism may include adetection of a rapidly time-varying emissions.

In certain aspects of the implementations, the detected emissionintensity indicates that the lased rock is spalling.

In certain aspects of the implementations, the emission intensityindicate a specified material removal mechanism if the emissionsfluctuate with a frequency above a specified threshold value.

In certain aspects of the implementations, adjusting the one or morelaser parameters may include changing beam irradiance of the laser inresponse to the optical response profile of the emissions detected fromthe lased rock.

In certain aspects of the implementations, detecting emissions from thelased rock may include receiving light from the lased rock for a periodof time.

In certain aspects of the implementations, detecting emissions from thelased rock may include detecting a steady emission intensity, the methodfurther comprising determining that the lased rock is not spalling basedon detecting the steady emission intensity. Certain implementations alsomay include determining that the rock is melting based on detecting thesteady emissions. In some implementations, it may be determined that therock is dissociating based on detecting the steady emissions.

In certain aspects of the implementations, lasing subterranean rock mayinclude perforating a sidewall of the well bore.

In certain aspects of the implementations, lasing subterranean rock mayinclude drilling the well bore.

In certain aspects of the implementations, the controller may include aprocessor communicatively coupled to the controller and configured toreceive signals from the detector and output emissions information tothe controller.

In certain aspects of the implementations, the controller is configuredto automatically adjust the irradiance of the laser energy when thedetected emissions from the rock indicate that the rock is notresponding as specified. In certain aspects of the implementations, thelight detected from the rock indicates that the rock is not spallingwhen the emissions have a varying intensity with respect to time below athreshold value.

In certain aspects of the implementations, the controller is configuredto maintain the power of the laser when the emissions detected from therock indicate that the rock is spalling.

In certain aspects of the implementations, the controller is configuredto determine that the rock is spalling when emission intensity detectedhas varying intensities with respect to time, the variations inintensities occurring with a frequency above a threshold value.

Certain implementations may include a reflector configured to reflect alaser beam towards the rock and to reflect the emission from the rock tothe light detector. Some implementations may include a dichroicreflector, the dichroic reflector configured to reflect a laser beamtowards the rock and to transmit the light emitted from the rock to thelight detector.

In certain aspects of the implementations, the optical detector mayinclude a spot detector.

In certain aspects of the implementations, the optical detector mayinclude a line detector.

In certain aspects of the implementations, the optical detector mayinclude a two-dimensional detector array.

The details of one or more embodiments of the present disclosure are setforth in the accompanying drawings and the description below. Otherfeatures, objects, and advantages of the disclosure will be apparentfrom the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a side cross-sectional view of an example laser tool inaccordance with the present disclosure depicted perforating a well bore.

FIG. 2 is a side cross-sectional view of an example laser toolconstructed in accordance with the present disclosure depictedperforating a well bore.

FIG. 3 is a schematic block diagram of an example controller.

FIG. 4A is side cross-sectional view of an example laser toolillustrating an adjustable reflector.

FIG. 4B is a top cross-sectional view of the example laser tool of FIG.4 a illustrating the adjustable reflector.

FIG. 4C is a side cross-sectional view of an another example laser toolshowing different trajectories of the laser beam typical in drilling avertical well bore

FIG. 4D is a side cross-sectional view of another example laser toolshowing different trajectories of the laser beam achieved using a fiberoptic array.

FIG. 5A is a schematic diagram of a laser beam spot and a projection ofan optical spot-detector location relative to the laser beam spot.

FIG. 5B is an example representation of the optical response of rockspallation.

FIG. 5C is a graphical representation of an example detector signalindicating spallation.

FIG. 5D is a graphical representation of an example detector signalindicating inefficient rock removal.

FIG. 6A is a schematic diagram of a laser beam spot and a projection ofan optical line-detector location off-set relative to the laser beamspot.

FIG. 6B is a schematic diagram of a laser beam spot and a projection ofan optical line-detector location intersecting the laser beam spot.

FIG. 6C is a schematic diagram of a laser beam spot and a projection ofa location of a two-dimensional configuration of an optical detector.

FIG. 7 is a process flow chart for controlling laser parameters based onthe optical response of a lased subterranean formation.

FIG. 8 is a graphical representation of laser power versus specificenergy of a rock delineating the spallation zone and the melting zone.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

High power laser technology may be used for drilling and perforatingdownhole hydrocarbon formations. The amount of energy required to removea given volume or mass of rock is defined as specific energy. Anefficient rock removal process will result in a low specific energywhile an inefficient process will exhibit a high specific energy. For aparticular rock sample, the specific energy required to cut or drillthrough it depends on the laser parameters applied. These parametersinclude irradiance, laser power, spot size, laser on time, purge time,delay time between laser off and purge on.

Rock is often not a homogenous, isotropic material and its propertiesand composition change from well to well and from one location within awell to another and localized changes in physical or chemicalcomposition, saturation, cracks or veins of dissimilar materials mayrequire changing of the laser parameters in order to initiate a laserdrilled hole and additional changes to the laser parameters may berequired “on the fly” as the laser cut hole into the rock progresses.

The present disclosure is directed to systems, methods, and apparatusesfor remotely detecting when laser drilling, perforating or other rockremoval processes are efficient or inefficient. If an existing set oflaser parameters results in inefficient removal, these parameters may beadjusted while the laser is down-hole until efficient removal isreestablished. In this way, a set of laser parameters resulting inefficient laser rock removal can be used at all times. This will resultin quicker, more cost effective laser rock drilling, perforating orremoval with improved hole geometry.

Several mechanisms exist for laser rock removal, including spallation,melting, dissociation, and vaporization. FIG. 8 is a graph 800 ofspecific energy versus average power (one of the laser parameters listedabove) for a representative sandstone sample. The vertical line 802 inFIG. 8 marks the transition in laser power where the rock removal regimechanges from spallation to melting. An abrupt increase in specificenergy when the removal method switches from spallation and melt starts.Efficient (low specific energy) rock removal can be achieved byadjusting the laser power to the maximum level where spallation occurs,but below the power threshold where melting begins. Usually, it isdesirable to operate in the power region where specific energy isminimum as shown in FIG. 8. Spallation is typically preferred tomaterial removal by melting because spallation has a higher energyefficiency and results in an easier handling of debris.

Similar plots can be made where other laser parameters are changed andthe remainder are held constant, however a general pattern emerges thatspecific energy increases when melting starts occurring.

Spallation and/or melting may be determined by the optical signature ofthe rock during laser illumination. The absorption of incident laserenergy can result in rapid local heating of the rock surface. A portionof absorbed energy is re-radiated from the target region in the form ofthermal emissions governed by Planck's law. Temperatures in excess of800 C. are commonly attained in tenth-second timeframes when subjectedto high power laser energy. Thermal emission's thus typically peak inthe visible or near-IR region of the electro-magnetic spectrum. Currentgeneration of high power lasers utilized in industrial applications arecapable of delivering very high quality beams with near Gaussianintensity profiles, especially if delivered via a long spatiallyfiltering fiber optic. Thermal emission from a flat, homogeneous rocksurface impacted with such a laser beam resembles a solid circularglowing spot. Thermal emission and incident beam intensity profiles arehighly correlated, with the region of brightest thermal emissioncoinciding with the peak of the incident beam profile. In practice,rough rock surfaces and non-uniform conductivity result in more complexthermal emission regions.

In the absence of material removal mechanisms, a constant incident laserpower would be expected to yield increasingly bright thermal emission atlower wavelength until the energy input and output balance and a steadystate temperature is attained. In practice, material removal processestypically initiate prior to obtaining steady state, provided asufficiently high power laser is employed.

Under the most desirable material removal conditions, the sudden energyinput resulting from laser incidence induces thermal stresses that shearrock grains and heat pore spaces in the rock matrix, causing grains andbits of rock matrix to be ejected from the surface. This condition isknown as spallation. The ejected material often exhibits strong visiblethermal emission signatures resulting in easy visual tracking of theseparticulates. The visual effect of observing many ejected grains rapidlymoving radially outward from a central bright region at the site oflaser incidence greatly resembles a type of burning firework known as a“sparkler”. A sparkler is a form of pyrotechnic comprised of a wirecoated with a mixture containing an oxidizer; a fuel (e.g. charcoal andsulfur); a metal powder (e.g. iron, steel or aluminum); and acombustible binder (e.g. starch or sugar). When ignited at one end ofthe wire, this pyrotechnic burns slowly and releases a shower of whitehot sparks.

Efficient spallation results in lower than otherwise observed thermalheating of the rock surface since much of the heated material is quicklyejected from the rock surface. Furthermore, this process typicallymaintains rock temperatures below the melt transition temperature. Assuch, key thermal emission signatures indicating spallation are adynamic, low average intensity, longer wavelength signal correspondingto relatively low rock surface intensity in the presence of visibletracers of ejecta moving outward from the point of laser-rockinteraction. FIG. 5B, discussed in more detail below, is an examplerepresentation of the optical image of rock spallation. In FIG. 5B, alaser is directed to the rock formation. The solidly glowing laser spot502 is shown at the center of the heated mass. An optical detector canbe positioned in a well tool so that it detects the optical response ofthe heated rock in a specified area. In certain instances, as shown inFIG. 5B, that specified projection location 554 is off-center from andnot encompassing the laser spot 502. However, in other instancesdiscussed in more detail below, the specified area can encompass thelaser spot 502 and can be of different shapes and sizes. The opticaldetector (e.g., discussed herein) can be used to detect spallation bythe white hot ejecta 556 coming off of the rock—looking for an erraticor irregular, unsteady optical response produced by the ejecta 556 asthey pass in and out of the specified area, momentarily lighting thearea or a portion of the area. See FIG. 5C. In certain instances, theoptical detector can be used to look for time dependent variations inthe optical response that occur with a frequency above a specifiedthreshold value determined to indicate spalling and/or a certainspecified degree of spalling.

In contrast, when the laser parameters result in rock melting, thevisual effect is different from spallation. When melt is occurring, nosparks are observed; instead, the optical response is a steadily glowingcenter where melted material tends to puddle in the center. Occasionalmelted rock may drip out of the hole, but generally, the light emissionobserved from melting is much less dynamic that that observed duringspallation. See FIG. 5D. The visual effect of dissociation is similar tothat of melt.

Dissociation is a process by which rock is heated and then wet. The rockmaterial can undergo a chemical reaction, turning the calcium carbonateinto CaO₂. The CaO₂ is soluble in water. In some instances, dissociationmay be desirable, and the optical response that indicates a rock that isundergoing dissociation can be identified using a detector to detect theemitted light from the rock.

The optical response of the lased rock can be detected and used toadjust laser parameters while the laser is down-hole. For example, anoptical detector can receive the light emitted from the lased rock, andthe variation in light intensity over time for a given spatial area ofreference can be used to determine whether spallation is occurring(e.g., a high variation in light intensity over time) or whether melt isoccurring (e.g., a low variation in light intensity over time) orwhether neither is occurring.

Turning to FIGS. 1 and 2, FIG. 1 is a side cross-sectional view of anexample laser tool 20 in accordance with the present disclosure depictedperforating a well bore. FIG. 2 is a side cross-sectional view of anexample laser tool 20 constructed in accordance with the presentdisclosure depicted perforating a well bore. A cased well bore 10 in asubterranean zone 12 has a casing 14 affixed therein. A layer 16 ofcement or similar material fills an annulus between the casing 14 andthe well bore 10. An illustrative laser tool 20 is depicted in useperforating the well bore 10. The illustrative laser tool 20 is adaptedto be inserted into the well bore 10 depending from a wireline 18(FIG. 1) or a tubing string 19 (FIG. 2), and direct a laser beam 26.Although depicted as removing material from the subterranean zone 12 toform a perforation 22, the laser tool 20 can be adapted to also oralternatively drill a new well bore, extend an existing well bore, orheat material to emit light for use in laser induced breakdownspectroscopy (LIBS). As the illustrative laser tool 20 of FIGS. 1 and 2is depicted perforating a cased well bore 10, it is directing the laserbeam 26 onto the casing 14, the cement 16 and the subterranean zone 12.The illustrative laser tool 20 and related concepts described herein areequally applicable to an “open hole” well bore. An open hole well boreis one in which at least a portion of the well bore has no casing.Furthermore, the laser tool 20 may be used in perforating or drillingthrough various equipment installed in a well bore, and is not limitedto perforating through casing, cement layers, and subterranean zone.When referring to a wall of a well bore herein, the wall can include anyinterior surface in the well bore, such as a sidewall or end/bottom wallthereof.

Power and/or signals may be communicated between the surface and thelaser tool 20. Wireline 18 may include one or more electrical conductorswhich may convey electrical power and/or communication signals. Wireline18 may additionally or alternatively include one or more optical fiberswhich may convey light (e.g. laser) power, optical spectra, and/oroptical communication signals. Neither the communication of power, norsignals to/from the surface, are necessary for the operation of theimplementations. In lieu of such communication, downhole batteriesand/or downhole generators may be used to supply the laser tool 20power. A downhole processor may be employed to control the laser tool20, with relatively little (as compared to wireline) or no communicationfrom the surface. For example, instructions for performing operationsmay be preprogrammed into the processor (ex. processor 44 in FIG. 3)before running the laser tool 20 into the well bore 10 and/or the lasertool 20 may respond to simple commands conveyed via surface operationssuch as rotary on/off, relatively low data rate mud-pulse,electromagnetic telemetry, and acoustic telemetry communication.

In implementations incorporating a tubing string 19, the tubing may becontinuous tubing or jointed pipe and may be a drilling string. Thetubing string 19 may incorporate a wireline 18 as described above.Tubing string 19 may be “wired drill pipe,” i.e. a tubing havingcommunication and power pathways incorporated therein, such as the wireddrill pipe. The tubing string 19 may contain a smaller tubing stringwithin for conveying fluids such as those used in the fluid based lightpath described below or for conveying chemicals used by the laser.

As discussed above, the laser tool 20 may be configured for use inanalyzing material using laser-induced breakdown spectroscopy (LIBS). InLIBS, at least a portion of the material being sampled is heated, forexample to a plasma or an incandescent state, and the wavelengthspectrum and intensity of the light it emits is measured to determine achemical characteristic of the material, for example, the chemicalelements of the material. The light may be in either or both of thevisible and invisible spectrums. The laser tool 20 can also beconfigured to determine a physical characteristic of the material, suchas its temperature or thermal properties. The laser tool 20 can operateto heat the rock of the subterranean zone 12 (or other material beinganalyzed) in situ, i.e. without removing the rock of the subterraneanzone 12, using laser beam 26 while the laser tool 20 is operating toremove material (drilling or perforating) or apart from operation of thelaser tool 20 to remove material.

If configured to both remove and analyze material, the laser tool 20 canbe configured to remove material and heat the material being removed orthe remaining material to emit light 36 during the same duty cycle orduring separate cycles. For example, the laser tool 20 can removematerial during a first duty cycle and operate to heat material, at thesame location or a different location, in a second duty cycle.

The power of the laser beam 26 can be equal from cycle to cycle, varyfrom cycle to cycle, or the laser beam can be fired in non-cyclicalpulses of varying power. For example, it may be desirable to use amulti-pulse technique to heat the subterranean zone 12 to enable use ofa lower powered laser than is necessary to heat the subterranean zone ina single pulse. In a multi-pulse technique, a first laser beam pulse isfired toward the material being analyzed to generate a cavity in thematerial and/or the interceding or surrounding materials, such as wellfluids and drilling mud, resulting from rapidly expanding vaporizedmaterial. A second, higher power pulse is then fired into the materialbeing analyzed to heat the material to a plasma or incandescent state.The multi-pulse technique may also encompass firing the first laser beamin a higher power pulse than the second laser beam pulse (e.g. forblasting away interceding material). Additional laser beam pulses may befired, of higher or lower power than the first and second laser beampulses, as is desired. For example, a third laser beam pulse may befired to perforate the subterranean zone rock.

As a heated portion of the subterranean zone may continue to emit lightfor a brief period of time after the laser beam has ceased beingdirected at the location, the optical detector 48 can be operated toreceive emitted light 36 either (or both) while the laser beam 26 isbeing directed at the location and afterwards, for example during an offcycle of the laser beam 26 or while the laser beam 26 is being directedto heat or remove material in a different location. It is also withinthe scope of the disclosure to re-heat the subterranean zone at sometime after the laser tool 20 has been operated to remove material at thelocation, and thereafter use the optical detector 48 to receive theemitted light 36.

In FIGS. 1 and 2, the illustrative laser tool 20 includes a laser beamdevice 24 that generates or relays a laser beam 26 into the subterraneanzone 12. The laser tool 20 may optionally be provided with a focusingarray 28 through which the laser beam 26 passes. The laser beam device24 may generate the laser beam 26, and thus may be an electrical,electro-chemical laser or chemical laser, such as a diode laser or anexcimer or pulsed Na:YAG laser, dye laser, CO laser, CO2 laser, fiberlaser, chemical oxygen iodine laser (COIL), or electric discharge oxygeniodine laser (DOIL). The laser beam device 24 may relay the laser beam26 generated remotely from the laser tool 20, such as a laser generatedby a laser generator 29 on the surface and input into the laser beamdevice 24 via a transmission line 27 (FIG. 2), such as an optical fiberor light path. In some implementations it may be desirable to use a DOILto increase service intervals of the laser tool 20, because a DOIL doesnot substantially consume the chemicals used in creating the laser beamand the chemicals need not be replenished for an extended duration. Itis to be understood that the examples of particular lasers disclosedherein are for illustrative purposes and not meant to limit the scope ofthe disclosure.

The laser beam may be pulsed, cycled, or modulated by pulsing, cycling,or modulating the control signal, and/or using an optical chopper,shutter, digital micro-mirror device, Kerr cell, or other mechanical,electrical, or photonics based light switching device to shutter, pulse,cycle, or modulate the emitted beam. In some implementations, the laserpulse duration may be on the order of 10 nanoseconds. A Kerr cell is oneelectro-optical device that may be used to provide shuttering on theorder of such speeds.

As discussed above, the laser beam 26 is generated by a laser 24. Thelaser beam 26 impinges a reflector 30 and is reflected towards the wallof the well bore 10. The laser beam 26 is directed through a window 54in the casing 14. The laser beam 26 then impinges the layers of the wellbore, as discussed above, to create the perforation 22. Put differently,lasing the subterranean rock includes perforating a sidewall of the wellbore 10.

When the laser beam 26 impinges on the rock, the rock may respondoptically. Light emitted by the rock can traverse a path towards thereflector 30 and towards optical detector 48. The optical response ofthe lased rock can be detected by the optical detector 48, which cansend signals to a controller 38 (described in FIG. 3), across acommunications path 50. The optical detector 48 can be configured toprovide a signal representative of the detected light to a controller38, and, in some instances, to a processor 44. Processor 44 can receivea signal or signals from the optical detector 48. The processor 44 canreceive, analyze, interpret, or otherwise process the received signal(s)from the detector, and make a determination as to whether the rock isspalling or melting (or neither). The processor 44 can also performFourier transforms on optical data and apply filters to the data. Theprocessor 44 can also automatically adjust the laser parametersaccordingly. The processor 44 can also display a graphical analysis ofthe intensity over time to an operator, who can manually adjust thelaser parameters.

In certain implementations, the optical detector 48 resides behind thereflector 30. As discussed above, reflector 30 may be dichroic, allowingthe laser beam 26 to reflect towards the window 54, while allowing theemitted light from the rock surface and ejecta to transmit through thereflector 30. In other implementations, the detector 48 may reside atother locations in the well bore (e.g., within or outside of a down-holetool). For example, the reflector 30 may reflect light from the ejectatowards the surface, and the detector can be positioned to detect lightreflected from the reflector 30.

Turning briefly to FIG. 3, FIG. 3 is a schematic block diagram of anexample controller 38. Controller 38 may reside down hole with the lasertool 20 or can reside at the surface and be in communication with thelaser tool 20 and other components of the laser tool 20, such asdetector 48. For example, the controller can receive optical informationfrom the detector 48 by an optical communications line 50 which conveysoptical measurements to the controller via either electrical and/oroptical signals. If the controller is located downhole, it may containthe optical detector 48 thus obviating the need for line 50. Thecontroller can communicate with the laser 24 and components on thesurface across a wireline 40. The controller 38 includes a processor 44and computer-readable media 46. The processor 44 can performspectroscopic analyses based on light received from the detector 48across optical communications line 50. The analyses can be stored oncomputer-readable media 46. The processor 44 and computer-readable mediacan communicate with surface equipment across wireline 40. In addition,the processor 44 can control the power of laser 24 based on thespectroscopic analysis. In certain implementations, the controller 38can communicate with laser generator 29, shown in FIG. 2, to instructthe laser generator 29 to vary the laser parameters, such as the laserpower, based on the spectroscopic analysis indicating a “melt” or rateof spallation optical response. The laser adjustments can be continuousand automatic. That is, the laser power adjustments can be made withouthuman intervention.

Returning to FIGS. 1 and 2, focusing array 28 may include one or moreoptical elements or lenses configured to focus the laser beam 26 at agiven focal length or adjustably focus the laser beam 26 to variousfocal lengths. Some examples of suitable devices for an adjustablefocusing array 28 can include one or more electro-optic lenses thatchange focal length as a function of voltage applied across the lens orone or more fixed lenses and/or mirrors movable to change the focallength. It is understood that there are many suitable devices formanipulating an optical beam which can be actively manipulated,responding to mechanical, acoustical, thermal, electrical or other formsof input energy and numerous such devices are within the scope of thedisclosure. The focusing array 28 focuses the laser beam 26 on thematerial being removed or heated.

Use of an adjustable focusing array 28 enables the laser beam 26 to bemore precisely focused on the material being removed or heated than afixed focusing array 28, for example, when there is movement of thelaser tool 20 relative to the subterranean zone 12. An adjustablefocusing array 28 also enables the laser beam 26 to be focused on theend wall of the material being removed as the end wall moves deeper intothe subterranean zone. In removing material, the laser beam 26 can befirst focused on the closest surface of the material to be removed thenadjusted to maintain focus as the surface from which material is beingremoved moves deeper into the material. In the case of perforating awell bore 10, the laser beam 26 can be first focused on the interior ofthe casing 14 and adjusted to maintain focus at an end wall of theperforation 22 as the perforation deepens through the casing 14, thecement 16 and into the subterranean zone 12. In heating a material beinganalyzed to emit light, the laser beam 26 can be focused on the materialbeing analyzed. The focal length and/or properties of the laser beam maybe actively manipulated, for example to compensate for movement of thelaser tool 20 relative to the material being heated or removed.

A length to the desired location can be determined using a distancemeter, such as an acoustic or optical distance meter, configured tomeasure a distance between the laser tool 20 and the material beingremoved or analyzed. That length can then be used in determining a focallength at which to focus the adjustable focusing array 28. Opticaldistance meter (or range finding) technologies are known, for exampleusing a laser beam and a photo diode to detect the light returned fromthe subterranean zone whose range is of interest wherein a modelablerelationship exists between the distance to be measured, the focal pointof the laser beam, and the intensity of the returns. By varying thefocal point of the beam and monitoring the intensity of the returns, thedistance to the subterranean zone may be inferred. Alternatively, adistance, relative distance, or change in distance may be inferred witha single focal point by correlating intensity to a model or experimentaldata, or monitoring intensity decrease or increase at different timesduring a process (e.g. the perforating) expected to result in a changein such distance. As another alternative, optical time domainreflectometry may be employed as is known to measure the time a flightof a pulse of light to and from the subterranean zone, from whichdistance may be determined. The laser beam used by the optical distancemeter 66 may be from a laser beam device 24 used for removing or heatingmaterial, or maybe a separate beam from a separate device.

When using a fixed focusing array 28, constraining the relativetool/subterranean zone movement so that the distance from the well bore10 wall to the fixed focusing array 28 remains fixed in relation to thefocusing array's focal length ensures that the laser beam 26 willmaintain the desired focus. In an adjustable focusing array 28, it maybe desirable to constrain relative tool/subterranean zone movement toreduce the magnitude of focal length adjustments necessary to maintainfocus. Relative laser tool/subterranean zone movement can be reduced bysizing the exterior of the laser tool 20 close to the diameter of thewell bore 10 or by providing the laser tool 20 with one or morestabilizer fins that project to a diameter that is close to the diameterof the well bore 10. Movement of the laser tool 20 relative to thesubterranean zone can be further reduced by providing one or moreextendable stabilizers, that can be selectively expanded to reside closeto or in contact with the wall of the well bore 10.

Although the laser beam device 24 can be oriented to fire directlytowards the material being removed or heated in one or moretrajectories, the illustrative laser tool 20 is configured with thelaser beam device 24 firing into a reflector 30. The reflector 30directs the laser beam 26 toward the subterranean zone 12 and may beoperated to assist in focusing the laser beam 26 or operate alone in(when no focusing array 28 is provided) focusing the laser beam 26 intothe material being removed. In the illustrative laser tool 20 of FIGS. 1and 2, the laser beam 26 is directed substantially longitudinallythrough the laser tool 20 and the reflector 30 directs the laser beam 26substantially laterally into the well bore 10. The laser tool 20 can beconfigured to fire the laser beam 26 in other directions, for example,down.

The laser beam 26 may be directed to remove material or heat variouspoints around the well bore 10 and in varying patterns. In anillustrative laser tool 20 having a reflector 30, the reflector 30 canbe movable in one or more directions of movement by a remotelycontrolled servo 32 to control the direction, i.e. trajectory, of thereflected laser beam 26. In a laser tool where the laser beam device 24fires directly into the subterranean zone 12 or in a laser tool having areflector 30, the laser beam device 24 can be movable by control servoto control the trajectory of the laser. In lieu of or in combinationwith a reflector 30, the laser beam can be directed into thesubterranean zone 12 using a light path (see FIGS. 4D, discussed below),such as a fiber optic, that may optionally be movable by control servoto control the trajectory of the laser beam. The light path may includemultiple paths, such as a fiber optic array, that each direct the laserbeam in a different trajectory. The multiple paths can be usedselectively, individually or in multiples, to direct the laser beam indifferent trajectories.

In the illustrative example of FIGS. 1 and 2, the laser beam 26 isdirected using the reflector 30 and control servo 32, rather than or incombination with moving the laser tool 20. The control servo 32 can beconfigured to move the reflector 30, at least one of, about alongitudinal axis of the well bore 10 (see FIG. 4A), about a transverseaxis of the well bore 10 (see FIG. 5B), or along at least one of thelongitudinal and transverse axis of the well bore 10. FIG. 4A depictsthe laser tool 20 firing the laser beam 26 through angle α about thewell bore longitudinal axis. Depending on the application, it may bedesirable to configure the laser tool 20 so that angle α may be as muchas 360°. The reflector 30 can be adjusted by angle A to achieve a laserbeam trajectory α. FIG. 4B depicts the laser tool 20 firing the laserbeam 26 through angle β about the well bore transverse axis. Dependingon the application, it may be desirable to configure the laser tool 20so that angle β may be as much as 360°. The reflector 30 can be adjustedby angle B to achieve a laser beam trajectory β. The laser tool 20 canbe appropriately configured so as not to fire the laser beam 26 uponitself. FIG. 4C depicts an illustrative laser tool 20 firing in multipletrajectories, through angle φ, typical for drilling a vertical well bore10. Depending on the application, angle φ may be as much as 360° and maybe oriented through 360° polar about the longitudinal axis of the lasertool 20. The reflector 30 can be adjusted by angle Φ to achieve a laserbeam trajectory φ.

FIG. 4D depicts a illustrative laser tool 20 that uses a light path 104comprised of multiple optical fibers 106 each oriented to fire in adifferent trajectory. The laser beam 26 may be directed through all ofthe multiple optical fibers 106 substantially simultaneously, or may bemultiplexed through the multiple optical fibers 106, for example, as afunction of duty cycle as is described below. Likewise, emitted lightcan be received through the multiple optical fibers 106 for use inmaterial analysis as is described herein. Although depicted with aspecified number of optical fibers 106 arranged vertically, the numberand pattern of the optical fibers 106 can vary. For example, only oneoptical fiber 106 can be provided. In another example, the pattern inwhich the optical fibers 106 are arranged can additional oralternatively extend circumferentially about the laser tool 20 to reachcircumferential positions about the well bore 10. The arrangement ofoptical fibers 106 can be configured to produce specified patterns inthe material removed, heated, and/or analyzed.

By directing the laser beam 26 relative to the laser tool 20, withreflector 30, light path 104, or otherwise, the laser tool 20 can remainin a single position (without further adjustments or reorientation) andremove or heat material in multiple locations around the well bore 10.Accordingly, the number of adjustments and/or orientations of the lasertool 20 during an entire operation are reduced. Physically moving thelaser tool 20 is time-consuming relative to adjustment of the lasertrajectory using the configurations described herein (ex. by movingreflector 30). Therefore, the ability to reach multiple trajectorieswithout moving the laser tool 20 reduces the amount of time necessary toperform operations (drilling, perforating, subterranean zone analysis).

According to the concepts described herein, the laser beam 26 can bemanipulated with multiple degrees of freedom and focal points to removematerial in many different patterns. So for example, a slice or thinwedge can be removed from the wall of the well bore 10, orthogonal toand along the length of the well bore 10, and orthogonal to asubterranean zone bedding plane, with a larger thickness at its distalend from the well bore 10, and exposing far more subterranean zonesurface than traditional perforating operations. The concepts describedherein enable a perforation hole to be shaped (such as by providingslots, rather than tubes or pits) to minimize fluid pressure down-draw.Multiple shapes can be envisioned within the implementations which maypromote hydrocarbon recovery rate, total recovery and efficiency.

In the illustrative laser tool 20, the laser beam 26 can be directed toremove or heat material circumferentially about the well bore 10 byactuating the control servo 32 to rotate the reflector 30 about alongitudinal axis of the well bore 10 and/or actuating the reflector 30to move along the transverse axis of the well bore 10. The laser beam 26can be directed to remove or heat material along the axis of the wellbore 10 by actuating the control servo 32 to rotate the reflector 30about a transverse axis of the well bore 10 or move along thelongitudinal axis of the well bore 10. The laser beam 26 can be directedto remove or heat material in an area that is larger than could beremoved in a single trajectory, by actuating the reflector 30 to rotateabout and/or translate along at least two axes, for example thelongitudinal and transverse axis. The laser beam 26 would then bedirected in two or more different trajectories to substantially adjacentlocations on the material being heated or removed. For example, bydirecting the laser beam 26 to project on the material being removed orheated at quadrants of a circle, the laser beam 26 can substantiallyremove or heat the material in a circular shape. By directing the laserbeam 26 in two or more trajectories at the same location, the laser tool20 can remove material to form a conical perforation having a largestdiameter at the opening or having a smallest diameter at the opening.Also, the laser beam 26 may be directed in one or more trajectories toform a perforation in the earth formation, and concurrently whileforming the perforation or subsequently, be directed in one or moretrajectories to widen the perforation. The laser beam 26 can also bedirected in two or more different trajectories to remove or heatmaterial of the earth formation in a substantially continuous area ortwo or more disparate areas.

The laser being directable can be also be used to drill more efficientlyand/or with unique hole characteristics, as compared to both the classicdrill-bit drilling and prior non-directable laser drilling. In drillingwith the laser beam 26, the laser beam 26 would be directed axiallyrather than radially, and the laser beam tool 20 would be conveyed onthe bottom of the bottom hole assembly in place of the drilling bit (seeFIG. 5C). The beam path may also be selected to achieve directionaldrilling. A circular path could be swept by the laser beam 26, cutting(for example by spalling) a thin annular hole, approximately equal to adesired hole diameter. The resulting “core” sticking up in the middlewould be periodically broken off and reverse circulated up the well bore10, for example up the middle of the drill string 19, to the surface.The core may be lased for removal, as well. Accordingly, the laserenergy is being used only to cut a small amount of rock (i.e. theannular hole). The same laser beam 26 directing configurations discussedabove in the context of perforating could be applied to drilling.Because the material removal is not resulting from a mechanical bitbeing rotated, a circular cross-section hole is not necessary. Forexample, the laser beam 26 could be directed to sweep out elliptical,square, or other hole shapes of interest.

Using the directionality of the material removal allows formation of aspecified hole or perforation section shape designed and executed forpurposes of enhanced production. For example the hole or perforation canbe formed in a rectangular, oval, elliptical, or other hole section witha longer axis aligned to expose greater (as compared to a circularcross-section) amount of the producing subterranean zone, or aligned toprovide greater exposure to an axis of preferred permeability, orpreferential production (or non-production) of oil, water, gas, or sand.Such specified hole or perforation section shape may be designed andexecuted for purposes of well bore or perforation stability, for examplea rectangular, oval, or elliptical shape being employed with a longeraxis aligned with the principal stress field, for increased stabilityand reduced tendency of collapse as compared to a circularcross-section.

The power of the laser beam 26 can be selected such that the duty cyclenecessary to remove the material in the desired manner (crack, chip,spall, melt or vaporize) and/or heat the material to emit light allowsenough time during off cycles of a given trajectory for the laser beam26 to be directed in one or more additional trajectories. In otherwords, if the duty cycle necessary to remove and/or heat the material inthe desired manner is 10%, the 90% off cycle can be utilized byre-directing the laser beam 26 to remove and/or heat material from oneor more additional positions in the well bore 10. The duty cycle for thevarious positions can be substantially equal or one or more of thepositions can have a different duty cycle. For example, the variouspositions may have a different duty cycle if one or more of thepositions are a different material, if it is desired to remove materialat a different rate in different positions, or if it is desired toremove material in one or more positions and merely heat material in oneor more different positions to emit light. The laser beam 26 can becycled or pulsed to achieve the required duty cycle or the laser beam 26can be continuous and moved from position to position to achieve theduty cycle for each respective position. In either manner, the lasertool 20 operates to multiplex removal of material in one or morepositions, for example to form one or more perforations 22,substantially concurrently. Likewise if it is desired to drill orperforate a hole that is larger than the laser beam 26 can form on asingle trajectory or that otherwise must be formed with two or moretrajectories, the same multiplexing technique can be used to removematerial in the two or more trajectories substantially concurrently.More so, one or more positions on the earth formation can be heated toemit light substantially concurrently using this multiplexing technique.

In a laser tool 20 configured to analyze material, the optical detector48 is provided to receive emitted light 36 from the subterranean zone12. In an embodiment that communicates with the surface, the opticaldetector 48 is coupled to the surface by a communication link 40. Thecommunication link 40 can be a fiber optic or light path forcommunicating data or light to the surface or can be an electrical orother type of link. The communication link 40 can be used to transmitwavelength spectra or signals indicative of wavelength spectra to thesurface for analysis (ex. analysis using a surface based spectrometerand processor for determining the chemical characteristics of thematerial being analyzed). In an embodiment where the optical detector 48determines the wavelength spectrum of the emitted light 36, the opticaldetector 48 can include a pyrometer and/or spectrometer 42 (FIG. 4). Inaddition to the spectrometer 42, if the optical detector 48 isconfigured to determine the chemical characteristics of the subterraneanzone 12 (i.e. perform the LIBS), the optical detector 48 includes atleast one processor 44. The optical detector 48 may contain memory orother computer readable media (hereinafter computer readable media 46)for logging the emitted light 36 wavelength spectrum information,logging the chemical and/or thermal characteristic information, and/orstoring instructions for the processor 44 to operate at least a portionof the method of operation described herein.

In the illustrative embodiment of FIGS. 1-2, the reflector 30 isdichroic and configured to reflect the wavelength spectrum of laser beam26 while passing other wavelengths. The laser beam device 24 isconfigured to emit a laser beam 26 in a wavelength spectrum that isdifferent than the expected wavelength spectrum of the emitted light 36.The optical detector 48 is thus configured to receive the emitted light36 that passes through the reflector 30. A lens assembly 49 can beprovided behind the reflector 30 axially aligned with the incomingemitted light 36 and adapted to focus the emitted light 36 into atransmission path 50, such as a fiber optic, to the optical detector 48.The optical detector 48 can include a lens assembly 49 having one ormore lenses, and optionally a filter, as is desired to condition theemitted light 36 before transmitting to the optical detector 48.Alternatively, the optical detector 48 can be configured to receive theemitted light 36 from a position adjacent the laser beam 26. In such anembodiment, the reflector 30 need not be dichroic, and the lens assembly49 has a filter configured to filter out the wavelength spectrum of thelaser beam 26.

Some or all of the components of the laser tool 20 can be encased in ahousing 52. The housing 52 has one or more windows 54 adapted to allowpassage of the laser beam 26 out of the housing 52 and emitted light 36into the housing 52. The size and shape of the windows 54 accommodatethe aiming capabilities of the laser beam 26 and receipt of emittedlight 36. The windows 54 are further adapted to withstand the elevatedpressures and temperatures experienced in the well bore 10. Someexamples of materials for constructing the windows 54 may be silica,sapphire, or numerous other materials of appropriate optical andstrength properties. The windows 54 may have anti-reflection coatingsapplied to one or both surfaces to maximize the transmission of opticalpower there-through while minimizing reflections. The windows 54 maycomprise a plurality of optical fibers positioned to direct the laserbeam 26 or collect emitted light 36 from multiple locations about thewell bore 10, for example the optical fibers may be fanned radiallyabout the laser tool 20.

FIG. 5A is a schematic diagram 500 of a laser beam spot 506 on a wall ofthe well bore and a projection of an optical spot-detector location 508relative to the laser beam spot 506. The projection of the opticalspot-detector location 508 shows the off-set position of the opticalspot-detector relative to the laser beam spot 506. The opticalspot-detector itself is located in the well bore and does not contactthe wall. Diagram 500 shows an outline of a perforation 504 in the wellbore surface 502, the outline of the perforation shown as having aradius 505. The laser beam spot 506 is shown having a radius 507. Theprojection of the spot-detector location 508 is shown to be at aspecified distance 509 from the laser spot 506. The diagram 500 is notdrawn to scale; however, the diagram 500 shows the position of theprojection of the spot-detector location 708 as “off-set” from theposition of the laser beam spot 506. The projection of the opticalspot-detector location 508 is off-set from the laser beam spot 506 toavoid saturation by the laser beam spot, which allows for the detectionof variations in the intensity of light. Spallation can be associatedwith light that is detected when, during laser irradiation, the receivedoptical signal from the spot-detector is erratic or noisy (that is, theintensity of the light detected varies unpredictably over time; see FIG.5B and FIG. 5C). Melt is associated with light that is detected when,during laser irradiation, the received optical signal from the spotdetector is steady (that is, the detected light does not varyunpredictably over time or the change in intensity over time is within athreshold value). An essentially monotonic, smooth increase in detectedsignal intensity is expected as target material heats to the point ofmelt, where-at material temperature will plateau as energy is consumedby the state transition. See FIG. 5D. If no light is detected, the laserpower may be too low for either spallation or melt. The laser power canbe adjusted accordingly in that instance by receiving a “no-spallation”signal and comparing the actual laser power to the theoretical laserpower shown in FIG. 8.

FIG. 5B is an example representation 550 of the optical response of rockspallation. The laser beam spot 552 is shown at the center of the lasedrock. The projection 554 of the optical detector is shown offset fromthe laser spot 552. Also shown in FIG. 5B is an example of sparks 556.The sparks are also shown to intersect the optical detector projection554. The sparks 556 represent ejecta from the lased rock formation, andwould intersect the optical detector projection 554 randomly andintermittently. Therefore, the intensity of the light detected by theoptical detector would also be random and intermittent. Detecting suchlight would indicate rock spallation.

FIG. 5C is a graphical representation 560 of an example detector signalindicating spallation. In graphical representation 560, detector signal(y-axis) is plotted against time (x-axis). First, the laser is activated562. When the rock is heated, the detector signal indicates an increasein light emitted by the rock by an increase in the amplitude of thesignal strength. If spallation occurs, the optical signal detected canresemble the erratic signal shown by 566, which indicates that the lightemitted by the rock is erratic and time varying. Spallation stops afterthe laser is turned off 568. The optical signal then degrades slowly asthe rock cools, indicating that the light emitted from the rock isgradually losing intensity 570. The detector level A1 572 indicates adetector intensity level for melt conditions, which is described in moredetail below in conjunction with FIG. 5D.

FIG. 5D is a graphical representation 580 of an example detector signalindicating inefficient rock removal. Inefficient rock removal mayinclude melt or dissociation. In FIG. 5D, the laser is activated 582.The light emitted from the rock increases, which is indicated on theplot by an increase in the amplitude of the detector signal. In thiscase, the amplitude of the detector signal exceeds the reference valueA1 572. In general, the peak amplitude for melt conditions is higherthan the amplitude for spallation. Additionally, during melt anddissociation, the peak signal does not vary erratically with time, as itwould during spallation. The steady intensity is indicated by arelatively flat curve 584. Though curve 584 is relatively flat, lowamplitude variations may be detected as the nature of the rock facechanges. The low amplitude variations may be below the detectionsensitivity of the detector, or may be out of scale given the peakamplitude of the detector signal. When the laser is turned off, thesignal drops off, indicating that the intensity of the emitted light isdecreasing. As the rock cools, the intensity of the light graduallyfades, which is indicated by the gradual decline in signalstrength/amplitude.

FIG. 6A is a schematic diagram 600 of a laser beam spot 506 and aprojection of an optical line-detector location 602 off-set relative tothe laser beam spot 506 by an amount 604 (from the center of the laserbeam spot 506). In some implementations, the optical detector can be aline-detector, as opposed to a spot-detector. The off-set allows theoptical detector to detect light from sparks emitted from thesubterranean formation during spalling with a darker baseline than ifthe projection of the line-detector location were located closer to thelaser spot 506. The distance should still be within a certain distanceto detect a sufficiently high density of light at a high enoughintensity to determine that spalling is occurring. The line-detector canbe considered as a “line” of optical detectors or a one ortwo-dimensional array of photo-detectors. The line-detector can detectlight across a larger area than a spot-detector. FIG. 6B is a schematicdiagram 650 of a laser beam spot 506 and a projection of an opticalline-detector location 652 relative to the laser beam spot 506. In FIG.6B, the projection of the line-detector location 652 is across the laserbeam spot 506. In this implementation, the line sensor will need to havea higher dynamic range when measuring across the center of theperforating tunnel than when measuring off center, outside of thecentral laser glow because of the constant and high intensity light fromthe laser spot 506 and the resulting glow emitted from the location ofthe subterranean formation lased by the laser.

FIG. 6C is a schematic diagram 660 of a laser beam spot 506 and aprojection of a location 662 of a two-dimensional configuration of anoptical detector relative to the laser beam spot 506. Two-dimensionaldetector configurations can track trajectories of ejecta propagatingoutward from the laser-rock interaction region. Additionally,two-dimensional detector configurations can count zero-crossings acrossa linear or circular line sensor. This implementation provides aquantized rate of spallation that can be further optimized by variationof cutting parameters. The detector projection 662 is shown to include adotted box 664. The dotted box 664 is a projection of the interactionregion, which may be an artificially drawn portion of the entiredetector or detector array. Sparks that cross the boundary of theinteraction region—entering the interaction region or leaving theinteraction region—can be counted. The spark trajectories can beextrapolated as well.

FIG. 7 is a process flow chart 700 for controlling laser parametersbased on the optical response of a lased subterranean zone. At theoutset, a counter is set to zero (C=0) (701). A set of laser parametersis selected and applied to a laser. A laser beam is directed to impingeon a subterranean rock formation to perforate the subterranean zone(702). Lasing the subterranean rock can include perforating the wellbore and/or drilling the well bore. The light emitted from the rockformation is detected for a period of time (704). A determination can bemade based on the detected light whether the rock removal is consideredto be efficient (706). For example, if the intensity of the lightdetected for a specified period of time at a specific location iserratic, noisy, irregular, or otherwise indicative of spallation, it canbe determined that spallation is occurring, in which case, the rockremoval is occurring efficiently. If the intensity of the light detectedfor a specified period of time at a specific location is steady or doesnot vary over time (or the variance of the intensity over time is belowa threshold value), then it can be determined that melt is occurring,dissociation is occurring, or, more generally, that spallation is notoccurring, and therefore, the rock removal is not occurring efficiently.In some implementations, spalling can be determined by detecting lightthat varies in intensity with respect to time, where the variation ofintensity is detected at a frequency above a threshold value. Forexample, light can be detected by the optical detector and signalsrepresentative of the detected light sent to a controller. The datacollected can be transformed from the time domain to the frequencydomain (e.g., using a Fourier transform). A high-pass filter can beapplied to the frequency-domain data, to filter any signals atfrequencies lower than a threshold value defined by the high-passfilter. The high-pass filter could be designed such that the resultingdata indicates the presence or absence of spalling—high volume dataabove the filter cut-off indicates spalling; low volume data above thefilter cut-off indicates lack of spalling.

If efficient rock removal is detected, then the counter can beincremented (C=C+1) (712). Laser parameters can be maintained or furtherrefined to optimize spallation signal strengths or rates, or overallprocess efficiency. A determination can then be made whether C=Cmax(714). Cmax is maximum number of laser shots or pulses for a particularlasing iteration. Cmax can be used to train the control system and canbe used to ensure that sufficient sample space of data is collected todetermine whether the rock removal is occurring efficiently. If thecounter does not equal a maximum value, then lasing continues and theperforation depth can be monitored (716). It can be determined whether adesired depth is achieved (716). If the depth has not been achieved, thelaser continues to perforate the well bore, and light detectioncontinues from (704). If the depth is achieved, the laser can stopperforating (720), and other processes can commence (including thosethat use the laser, such as spectroscopic analyses).

If the counter is equal to its maximum value (and efficient rock removalis detected), then the counter is reset to zero (C=0) (708). The laserparameters can be adjusted (710). In this case, the laser parameters canbe adjusted so that a new lasing area is chosen or new laser parametersare selected to test whether efficient rock removal can be achievedusing different parameters.

If rock removal is determined to be inefficient (e.g., no spalling isdetected), then the counter is reset to zero (C=0) (708). The laserparameters can be adjusted (710). The laser parameters include, amongother things, laser power, irradiance (power/unit area), purge delay,orifice size on purge lance, purge velocity, the number of purges, etc.Laser power can be reduced to a point below that which would cause melt(see FIG. 8) or can be increased to enter the spallation zone. Theactive laser power can be compared to theoretical values, such as thosepresented in FIG. 8. The laser can then be started again to continue theprocess (702).

Other parameters can also be varied. For example, laser irradiance canbe varied be changing the laser power or by changing the spot size areausing lenses. The laser delay can also be varied. Delay may allow themelted rock to cool and solidify. The solidified rock can be removed toexpose a “clean” rock surface for further lasing and removal. Cycledelay can also be varied (that is, the time between lasing and purging).

Various configurations of the disclosed systems, devices, and methodsare available and are not meant to be limited only to the configurationsdisclosed in this specification. Even though numerous characteristicsand advantages have been set forth in the foregoing description togetherwith details of illustrative implementations, the disclosure isillustrative only and changes may be made within the principle of thedisclosure. Accordingly, other embodiments are within the scope of thefollowing claims.

What is claimed is:
 1. A method for removing subterranean rock with alaser, the method comprising: from inside a well bore, lasingsubterranean rock around the well bore; detecting emissions from thelased rock; determining whether the detected emissions from the lasedrock indicate a specified material removal mechanism; and if thedetected emissions do not indicate the specified material removalmechanism, adjusting one or more laser cutting parameters untilemissions detected from the lased rock indicates the specified materialremoval mechanism.
 2. The method of claim 1, further comprisingassessing an optical profile of the emissions detected from the lasedrock for characteristic properties of the specified material removalmechanisms.
 3. The method of claim 2, wherein a characteristic propertyof a specified material removal mechanism comprises a detection of arapidly time-varying emissions.
 4. The method of claim 2, wherein acharacteristic property of a material removal mechanism comprises adetection of steady emissions.
 5. The method of claim 1, wherein thedetected emissions indicate that the lased rock is spalling.
 6. Themethod of claim 1, wherein the emission intensity indicate a specifiedmaterial removal mechanism if the emissions fluctuate with a frequencyabove a specified threshold value.
 7. The method of claim 1, whereinadjusting the one or more laser parameters comprises, in response to theemissions detected from the lased rock, changing one or more of beamirradiance of the laser, laser power, laser spot size, laser on time,purge time, or delay time between laser shut-off and purge turn-on. 8.The method of claim 1, wherein detecting emissions from the lased rockcomprises receiving light from the lased rock for a period of time. 9.The method of claim 1, wherein detecting emissions from the lased rockcomprises detecting a steady emission intensity, the method furthercomprising determining that the lased rock is not spalling based ondetecting the steady emission intensity.
 10. The method of claim 9,further comprising determining that the rock is melting based ondetecting the steady emissions.
 11. The method of claim 10, furthercomprising determining that the rock is dissociating based on detectingthe steady emissions.
 12. The method of claim 1, where lasingsubterranean rock comprises perforating a sidewall of the well bore. 13.The method of claim 1, where lasing subterranean rock comprises drillingthe well bore.
 14. A well apparatus for rock removal, comprising: alaser tool configured for insertion into the well and to direct laserenergy onto rock; a detector configured for insertion into the well andto detect emissions emitted from the rock; and a controller configuredto adjust power of a laser based on emissions detected from the rock.15. The apparatus of claim 14, wherein the controller comprises aprocessor communicatively coupled to the controller and configured toreceive signals from the detector and output emissions information tothe controller.
 16. The apparatus of claim 14, wherein, when thedetected emissions from the rock indicate that the rock is notresponding as specified, the controller is configured to automaticallyadjust one or more of an irradiance of the laser energy, laser power,laser spot size, laser on time, purge time, or delay time between lasershut-off and purge turn-on.
 17. The apparatus of claim 16, wherein thedetected emissions from the rock indicates that the rock is not spallingwhen the emissions have a varying intensity with respect to time below athreshold value.
 18. The apparatus of claim 14, wherein the controlleris configured to maintain the power of the laser when the emissionsdetected from the rock indicate that the rock is spalling.
 19. Theapparatus of claim 14, wherein the controller is configured to determinethat the rock is spalling when emission intensity detected has varyingintensities with respect to time, the variations in intensitiesoccurring with a frequency above a threshold value.
 20. The apparatus ofclaim 14, further comprising a reflector configured to reflect a laserbeam towards the rock and to reflect the emission from the rock to thedetector.
 21. The apparatus of claim 14, further comprising a dichroicreflector, the dichroic reflector configured to reflect a laser beamtowards the rock and to transmit the light emitted from the rock to thedetector.
 22. The apparatus of claim 14, further wherein the detectorcomprises one of an optical spot detector, an optical line detector, ora two-dimensional array detector.
 23. A well laser system for use in asubterranean well comprising: a laser apparatus configured to: produce alaser beam, and direct the laser beam towards a subterranean rock; anoptical detector configured to detect light emitted from the rock; and acontroller communicatively coupled to the optical detector, thecontroller configured to: receive a signal from the optical detector,determine from the signal whether the rock is responding as specified;and adjust a parameter of the laser if the rock is not responding asspecified.
 24. The system of claim 23, wherein the controller comprisesa processor configured to receive signals from the optical detector andoutput instructions to the controller to adjust the power of the laserif the rock is not responding as specified.
 25. The system of claim 23,wherein the controller is configured to automatically adjust the powerof the laser when the light detected from the rock indicates that therock is not spalling.
 26. The system of claim 25, wherein the controllerdetermines that the rock is not spalling when no sparks are detected bythe optical detector.
 27. The system of claim 26, wherein the controllerfurther determines that the rock is dissociating when the light detectedis a steady glow.
 28. The system of claim 26, wherein the controllerfurther determines that the rock is melting when the light detected is asteady glow.
 29. The system of claim 23, wherein the controller isconfigured to maintain the power of the laser when sparks are detectedby the optical detector.
 30. The system of claim 23, wherein the laserapparatus further comprises a dichroic reflector, the dichroic reflectorconfigured to reflect a laser beam towards the rock and to transmit thelight emitted from the rock to the optical detector.
 31. The system ofclaim 23, wherein the optical detector comprises a spot detector. 32.The system of claim 23, wherein the optical detector comprises a linedetector.
 33. The system of claim 23, wherein the optical detectorcomprises a two-dimensional detector array.